All the more reason to use a pack protection module that monitors (and responds to) cell voltage differences.
Without reading his/her dissertation, I'm not sure what (s)he's measuring. What does (s)he define as a fully discharged cell, and how does (s)he achieve that state?
The modules we used certainly did. There was a connection to each series connection node. (And in assembly the connections had to be made in the correct order.)
That is exactly what the module preempted.
See Pg 24 (section 2.2.2). He lists 3 methods along with their limitations. I think (not sure) he's using coulomb counting (amp-hrs). Section 2.2.3 follows with capacity measurement, which is necessary to calculate the SOC. There's too much to quote. However, you wanted the discharge point, and that's not covered directly. He hints at: For lead acid and lithium-ion batteries, the relationship between the stabilized open circuit voltage, Eocs, and the SOC is approximately linear (Wang & Stuart, 2002). which implies that he uses 100% SOC as one point and extrapolates a linear plot to zero SOC somewhere on the knee of the curve. However, he also notes that it's temperature dependent, has hysteresis, and requires substantial time to stabilize the terminal voltage. Unless I missed something, he doesn't really specify how to measure the knee.
I won't pretend to understand all of it, especially since I'm buried in work tonight and am having problems with (paying) distractions. Maybe tomorrow.
OK, I'm impressed(1). That's the way battery packs should be built and monitored. However, why stop at monitoring individual cells? I prototyped NiCad and NiMH battery packs where each cell was also charged individually. It's (fairly) well known that you can charge these cells at almost any rate, as long as they're under 100% SOC. Go over even slightly, and the cell gets very hot, very quickly. I've built simulated chargers to do this and was able to charge NiCads successfully at up to 20C (20 times rated capacity) to about 95% SOC. Incidentally, the failures were rather impressive, including 2 small fires, which might explain why such fast charging is not commercially acceptable. I'm tempted to try the same tests with Li-Ion, but have not been sufficiently inspired or bribed to do so.
(1) Note: I'm not easily impressed.
-- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com jeffl@cruzio.com # http://www.LearnByDestroying.com AE6KS
KISS is often a euphemism for "cheap".
True. There are probably some safety issues involved. It would not do to have the customer twiddle the charging characteristics and potentially turn the battery pack into a incendiary or explosive device.
Nope. There's also the possibility of creative testing. The applications mix used for testing battery life by MobileMark 2007:
has a huge effect on measured battery life. However, there's nothing standard about the selection of test apps, which could easily be tweaked by the equipment vendor. I'm starting to see this with Netbooks, where fairly long battery run times are predicted, but rarely demonstrated. I had an Acer Aspire One (9" screen) and currently an Asus 700. Neither has come close to the rated run time when I use them normally at a local coffee shop.
Good. That covers the vendor in case anyone actually tests for the claimed capacity or run time.
Just thinking about it, there's enough info here to build a table or graph of the calculated battery life versus run time terminating at different EOC's. As you note, the closer to depletion I run the battery pack, the shorter the battery life (measured in charge cycles).
Well, yes. The frequency and transient response of these meters is rather lousy. My guess(tm) is that it has to be about 10 times lower than the 50/60Hz it's trying to measure. That would put it at about
5Hz (200msec), which is not all that horrible. Also, the filter caps in the typical laptop will smooth out most transient current spikes so that the meter never sees the spikes. I don't have a power line impairment tester to check this, but can probably trace out the schematic to see how it works. Here's the patent with block diagram and description:The top photo is the inside of the older 4 button version. The lower photo is the current 5 button version:
Litigatory trivia:
-- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com jeffl@cruzio.com # http://www.LearnByDestroying.com AE6KS
Remember these are industrial applications, NOT pooters.
Whoa, where did I say that? IMOE there is no discharge end impact on cycle life.
(snip rest)
I haven't really got the time to dig into the diss, but the expression "A direct correlation was found between the cell capacity and the open-circuit voltage of a fully discharged cell." doesn't make any sense. If you define a fully discharged cell as one which has been discharged to a pre-defined end-point (voltage), then all cells would have the same EOD voltage except for rebound. Or is THAT what he is getting at?
It is more about safety than extracting maximum life/performance from the packs. That's why these were termed "pack protection modules". They provided:
(a) over-voltage cutoff (b) excess charge current cutoff (c) excess discharge current cutoff (d) cell voltage imbalance cutoff (e) undervoltage cutoff
clearly aimed at protecting the pack (and manufacturer) from hazardous situations.
Because Ni-XX chemistries are current-mode charged, and actually over-charged, that of itself provides a measure of SOC equalisation which really makes it unnecessary to get involved in individual cell charging in series strings. This was disucssed in a recent thread on equalising SOC. Current-mode charging -> series cell equalisation if overcharged. Voltage mode (i.e. Li-XX) charging -> parallel cell equalisation.
Probably not worth the effort *if* the replication of charging circuits adds much complexity.
Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:
However, an unscheduled shutdown during an update to the directory (or other vital) sectors does seem to be one cause of 'file xxxx.xxx not found' BSOD computers that are brought to me to fix.
-- bz 73 de N5BZ k please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set.
I don't that very often, usually because I tend to do pre-emptive replacements of hard disks (based on various criteria ranging from S.M.A.R.T. reports to Ouigi board warnings). When I do see it, the hard disk is usually ready to fail. Unfortunately, it tends to trash files that Windoze like to scibble to constantly (i.e. the registry).
Also, some software that claims to speed up the machine turns on HD write-caching. Bad idea.
Worse are PATA and SATA drives with a large (32MB) cache on the HD. These do cache writes and will trash anything left un-flushed in the cache if the power fails. Moral: the bigger they are, the harder they crash.
Same with pulling the plug on USB, eSATA, and FireWire external drives. Lots of ways to trash data, all of which apply equally to FAT32. Despite these and other possible problems, NTFS journaling is a major improvement over FAT32 and should be used whenever possible.
-- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com jeffl@cruzio.com # http://www.LearnByDestroying.com AE6KS
Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:
disfortunately, the grad-student owned machines only get brought to my attention when they are infested or crashed. (one machine had over 50,000 virus infected files! "My machine is running slow.") Budget and personnel restraints prevent us from doing regular PM on most state owned machines. However, as part of my normal 'virus clean up' (often backup data, reformat, reinstall OS is the fastest and safest method) I do check the hard drives for signs of impending failure.
Agreed, although one of my cow-orker swears by the latest EFTn file system.
-- bz 73 de N5BZ k please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set.
The most I've seen is about 2,500 files. However, I rate my infected machines by the number of different viruses, worms, and spyware types found (not including cookies) that are actively running. No points for counting infected emails that haven't run. So far, about 20 different types is the worst I've seen where the machine is still sorta running.
Well, I have a partial solution. Keep the user out of places they shouldn't be playing.
It wasn't really designed for the purpose, but it's sufficient to prevent total beginners, arrogant grad students, and ivory tower professors, from trashing the operating system. Plenty of other solutions, but this is the one I like. As soon as they shutdown, the computer returns to its original state. Once a month, the PC goes into the shop for an update, lube job, and oil change. I have it installed at 2 car wash kiosks and one middle skool classroom. Other than having to establish an update regime, it works well.
Actually, you don't really need to install MS Steady State on every laptop in your system. Just one or two and the word will get around. After that, merely the threat of having it installed should be sufficient to inspire the students to clean up their act.
Also, you're being too nice. Make it clear that they are responsible for their own data backups. If they bring a machine to you for cleanup and disinfection, they should assume that it will be wiped and reloaded from scratch.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:
...
University policy and academic freedom.... My authority is rather limited when it comes to student owned computer or computer under the authority of various professors. Also, many of the computers I deal with are controling very expensive intruments. The main problem in those cases is keeping them from putting such machines on the internet.
Would work well in a room with 50 similar computers. We don't have any (though other departments do) such setups.
When I am talking about someones years of research, I warn them to back up everything, I ask if it is ok to wipe their drive if needed, I make an image of the drive before I do anything to it, AND I restore all their data that can be recovered!
I tell everyone about a guy I knew that had 9 years of research data in his car (paper notes) and his car caught fire and burned. He never finished his research and a few years later, he blew his brains out.
The lesson, I tell them, is 'make backups', 'make frequent backups', 'make multiple backups' and 'keep your backups in a different place from where your computer is located.'
It is bad enough to have to tell someone "I am sorry, I can't recover anything from your [hard|thumb] drive. There are companies that, for hundreds or thousands of dollars, will disassemble it and attempt to recover your data. Is it THAT important to you?"
I would much rather have someone say "thank you SO much for saving my data" than "you ruined my life", or going 'postal'.
-- bz 73 de N5BZ k please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set.
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